A wall clock moves 10 minutes fast in every 24 hours. The clock was set right to show the correct time at 8:00 a.m. on Monday. When the clock shows the time 6:00 p.m. on Wednesday, what is the correct time ?
- (a) 5:36 p.m. ✓ UPSC's answer
- (b) 5:30 p.m.
- (c) 5:24 p.m.
- (d) 5:18 p.m.
Why the answer is (a)
• From 8:00 a.m. Monday to 6:00 p.m. Wednesday the clock shows 58 hours (48 + 10).
• The clock gains 10 minutes in every 24 hours, so it shows 24 hours 10 minutes (1450 minutes) for every 1440 real minutes.
• Real time elapsed = 58 × 60 × 1440 ÷ 1450 = 3480 × 144 ÷ 145 = 3456 minutes = 57 hours 36 minutes; the clock has gained 24 minutes.
• 8:00 a.m. Monday + 57 hours 36 minutes = 5:36 p.m. Wednesday, option (a).
Why the other options are wrong
- (b) 5:30 p.m.
- 5:30 p.m. would mean the clock gained 30 minutes, but it gains only 24 minutes over this period.
- (c) 5:24 p.m.
- 5:24 p.m. would mean a gain of 36 minutes, but the gain is 24 minutes.
- (d) 5:18 p.m.
- 5:18 p.m. would mean a gain of 42 minutes, but the gain is 24 minutes.
Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2019, held on 2 June 2019. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.